Coupling transformer for television arrangements



Jano 9, 1940. K. SCHLESINGER 2,136,932

COUPLING TRANSFORMER FOR TELEVISION ARRANGEMENTS Filed May 12, 1957 fmenfar':

r0 r1 12 1'; Mil:

Patented an. 9, 194 f I g V [2 186 932. I

UNITED STATES PATENT. v oFnc- COUPLING TRANSFORMER Fen TELEVISION 1 IARRANGEMENTS Kurt Schlesinger, Berlin, Germany, 'a ssignor, bymesne'assignments, to Loewe Radio, Inc., a corporation of New YorkApplication May 12, 1937, Serial No. 142,167

. Germany May 16," .1936

5 Claims. (01. 178-44) The present invention relates to a" coupling 9and It respectively. via a condenser. .In additransformer for use inamplifier circuits for amtion the primary coil and the secondary coilare plifying very wide frequency-bands particularly each damped b y-aresistance H and i2 respecfor intermediate frequency amplifiers forteletivelyl vision reception or transmission, which transy reas n Of thepe Circuit arrangement 5 former complies with the requirements existngof the transformer coils'in accordance with the in such circuitsoperating with a good amplificainvention and its primary coils situatedon eithertion for a very large width of frequency. band. side of thesecondary coil in sihgle-layerfashion v The sub-jectmatter of thepresent invention reas set. forth in Fig. 1 there is obtained a verylates not to a transformer with purely inductive considerable broadeningof the frequency reb coupling, but to a transformer with a combinedsponse hand and an improvement of the transinductive-cap'acitativecoupling effect, which is mission in the range of the higher side bandadjusted by special arrangement of the windings frequencies, necessaryfor obtaining a large widt and the circuit. Further, the transformer2.0- of band. cording to the invention makes use of the phe- Theconnection between the windings are 15 nomenon of the two coupling wavesin the case shownin a simplified form in Fig. 2. The point i of a verytight coupling, and employs accordingly designates the high-potentialend of the pri a tight coupling of such nature .that the spacing mary;the primary winding coils 4 and 5 are of the two coupling wavescorresponds to the connected in series, and the point IE designateswidth of frequency band to be transmitted. In that end of the primarywhich is earthed. The 29 accordance with the invention in a high-fre-'primary current, flowing from the anode of valve quency circuit for theuniform amplification of 2, passes in the caseof high frequencies notonly very wide frequency bandsmore particularly for to the primarywinding 5, but at the" same time television purposes the couplingarrangement repalso for a largepart by way of the stray capacity resentsa transformer having windingsconnected I3 to the secondary coil 6. p InFig. 2 the line cur- 25 with each other ina definite manner consistingof rent is designated by Hi and the reactance culicoils arrangedcoaxially in'single-layer fashion on rent produced by the capacity 13isdesi'gnated the same axis the primary of which is divided by 15. Byreason of this proportion of reacinto two winding-coils arranged oneither side of tance current l5 there results in the secondary 30 thesecondary and wound in the same direction. winding, which is earthed at9, an additional drop The invention will be clearly understood by way inpotential which with-the statedpolarity assists of example shown in theaccompanying drawing the induced potential. The signs of both poteninwhich: tials are the same and opposite to the signof Fig. 1 shows atransformer arrangement acthe potential at the primary terminal 1.cording to the invention connected between two Thefleffect of this'capacitative auxiliary cou 35 amplifiertubes. pling .via capacity It isshown in the curves a Fig-2 is a simplified form of Fig. 1 and shows andb in Fig. 3, wherein the ordinate represents the additional capacitativecoupling effect bethe transmission degree and on the abscissa tweenprimary and secondary and k there are plotted the single frequencies tobe 4o 7 Fig. 3 shows several frequency curves from transmitted. Thecurve b is the transmission v4o which the efiect'of the couplingarrangement accurve obtained over the whole frequency band for cordingto the invention maybe recognised; the polarity of the connectionsaccording to Fig;

In'Fig. lthe coupling transformer l is shown 2 and curve a is thetransmission curve obtained in'conjunction with two tubes 2 and 3. Thecon when the connections to the secondary winding pling transformerconsists of a primary winding, 6 are. reversed. The resistances i! andi2 are 5 which is divided into two winding coils 4 and -5 omitted inboth cases a and b. The curve 0 is and a Secondary winding 1 l threendproduced by using damping resistances. I

ings 4, 5 and-6 are wound in the same direction. I The-band widthcovered by the transformer is According to the invention, thehigh-potential determined by the degree of inductive coupling ends o ePrimary half 5 a d 0 the co d ry between the primary windings 4,5 andthe sec- 50 8 are situated immediately adjacentto the secondaryfi. Therequired degree of coupling may ondary coil B.- Accordingly that end ofthe pri-. ,be attained with the transformer according 'to mary winding 5beginning at l isarran'ged close the invention having three co-axiallydisposed to that end of the secondary beginningat 8. coils by suitableadjustment of the axial lengths a. The secondaryand primary coils areearthedat of the coils by suitably selecting the diameter of the wireemployed. The magnitude of the capacitive coupling is determined mainlyby the distance a between coils 5 and 6. In accordance with theinvention, it may, if desired, also be adjusted by displacing over saidcoils an insulated ring 45 of conductive material, which is slotted inone place along a plane passing through its axis for avoiding eddycurrents.

The tuning of the two windings is effected by so dimensioning the coilsthat with their selfcapacities and the valve capacities and straycapacities they resonate at the desired frequency. All unnecessaryparallel capacities are avoided by making the capacities of thestructure and the supply conductors as small as possible. The smallerthese are, the greater may be chosen the self-inductance bycorresponding increase of winding-turns, and accordingly the greater isthe amplification which can be attained. The tuning of the coils takesplace initially in single fashion on the same wave in respect of theprimary and secondary coils. The splitting up into coupling waves occursby very tight coupling. The degree of amplification is determinedroughly by the slope S of the valve characteristics by the amount of thedetrimental anode capacity of the valves, by the carrier frequency f andby the frequency band width B to be transmitted, which in the carrierfrequency method appears as double width of band in the spacing of theside frequencies.

When operating with constant primary potential both peaks of thefrequency curve a. according to Fig. 3, in the case of properconnection, and of the frequency curve b in the case of reverse polarityof the secondary have the same height. When employing screening gridtubes, however, which alone preferably are used, the transformer isexcited not at constant potential (case of idle running), but atconstant radiofrequency current (case of short-circuit) In this case theradio frequency across the terminals of the primary winding 4, 5 is notconstant but varies with the frequency dependent upon the impedance ofthe primary winding 4, 5, which impedance again has the character of aresonance curve. In this way the radio frequency potential producedacross the secondary winding is increased in the neighbourhood of theresonance frequency of the primary winding with the result that theresultant overall response curve has two'peaks of unequal height. Thiseffect is very disturbing when a plurality of these units are connectedin cascade, because the resonance peaks of the successive stages becomemultiplied together. In practice, therefore, any method which enables anapproximation to the ideal frequency curve of the single transformer tobe obtained is very important. For this purpose in the circuitarrangement according to the present in vention the following measuresare most advantageous and most important.

1. Adjustment of the damping resistance ll lying in parallel to theprimary side, in such manner as to have a value being smaller than theprimary impedance of the transformer in the frequency band employed. Inthis way there is certainly a loss of amplification, but one obtains anapproximation to the state of idle running and the transformer isexcited at substantially constant primary potential.

2. Disposal of the natural wavelength of the secondary coil in the waverange, i. e., in the range of the higher side-band frequencies, in orderto permit there of an increase of the resuiting frequency curve. Thismethod requires to be adopted only to small extent to be successful, asa small displacement of the resonant range of the secondary coil intothe short-wave range has the double effect of improvement in this rangeand a deterioration in the long-wave range, i. e., in the range of thelower side-band frequencies. The secondary coil is clamped only to suchextent by a resistance I2 that the same has no further oscillatoryproperties (aperiodic damping: w'L=R). The damping by the resistance l2may be much smaller than the damping by resistance H The frequency curve0 according to Fig. 3 is practically attained for a coupling transformeraccording to Fig. l by using following data:

Number of image lines: 400.

Width of frequency band 2.25 megacycles.

Carrier frequency 7.5 megacycles.

Primary damping resistance 11:2,000 ohms.

Primary inherent parallel capacity approx. 15

Secondary damping resistance 12:5,000 ohms.

Natural wave lengths: primary=7.5 megacycles.

Secondary=8 megacycles.

Length of winding for all three coils approximately 2-3 mm.

The curves a and b set forth in Fig. 3 are attained without usingdamping resistances, and clearly show that the long-wave maximum ishigher than the short-wave maximum. The curve 0 in Fig. 3 shows theresult of the correcting measures according to the invention. Thecapacitative coupling may be governed by the spacing a and the inductivecoupling by the spacing b. In this way the two peaks of the frequencycurve may be made of equal height.

I claim:

1. A high frequency transformer for coupling amplifier circuits used foruniform amplifying of very wide frequency bands, more particularly fortelevision purposes comprising a primary and a secondary windingconnected between the circuits to be coupled and coupled so tightly asto have a wide frequency resonance curve corresponding to the desiredwidth of frequency band produced by reason of the arising two couplingwaves, said primary and secondary coils the resonant frequencies ofwhich are determined by the inherent capacities being arranged insingle-layer fashion co-axially on the same axis, said primary beingdivided into two winding coils arranged on either side of the secondaryand wound in the same direction, the high potential ends of one of saidprimary coils and of the secondary being arranged closely to one anotherso that the additional capacity coupling between said one primary coiland the secondary is more efiective between said one primary coil andsaid secondary than between the other primary coil and said secondary.

2. A high frequency transformer for coupling amplifier circuits used foruniform amplifying of very wide frequency bands more particularly fortelevision purposes comprising a primary and a secondary windingconnected between the circuits to be coupled and coupled so tightly asto have a wide frequency resonance curve corresponding to the desiredwidth of frequency band produced by reason of the arising two couplingwaves, said primary and secondary coils the resonant frequencies ofwhich are determined by the inherent capacities being arranged insingle-layer fashion co -axially on the same axis, said primary beingdivided into two Winding coils arranged on either side of the secondaryand wound in thesame direction, the high potential ends of one of saidprimary coils and of the secondary being arranged closely to one anotherso that the additional capacity coupling between said one primary coiland the secondary is more effective between said one primary coil andsaid secondary than between the other primary coil and said secondary,said windings being arranged movable in their situation one relative tothe other for varying the spacing between primary and secondary.

'nant frequencies of which are determined by the inherent capacitiesbeing arranged in single-layer fashion co-axially on thesame axis, saidprimary being divided into two winding coils arranged on either side ofthe secondary and wound in the same direction, the high potential endsof one of said primary coils and of the secondary being arranged closelyto one another so that the additional capacity coupling between said oneprimary coil and the secondary is more effective between said oneprimary coil and said secondary than between the other primary coil andsaid secondary, said windings being arranged movable in their situationone relative to the other for varying the spacing between primary andsecondary and said primary having in parallel with its terminals anohmic resistance, which is smaller than the smallest impedance betweenthe primary terminals, the secondary coil being aperiodically damped.

i. A high frequency transformer for coupling amplifier circuits used foruniform. amplifying of very wide frequency bands, more particularly fortelevision purposes comprising a primary and a secondary windingconnected between the circuits to be coupled including inherent circuitcapacities and coupled so tightly as to have a wide frequency resonancecurve corresponding to the desired width of frequency band produced byreason of the arising two coupling waves, said primary and secondarycoils being arranged in singlelayer fashion co-axially on the same axis,said primary being divided into two winding coils arranged on eitherside of the secondary and wound in the same direction, the highpotential ends of one of said primary coils and oi.- the secondary beingarranged closely to one another so that the additionalcapacity couplingbetween said one primary coil and the secondary is more effectivebetween said one primary coil and said secondary than between the otherprimary coil and said secondary, said windings being arranged movable intheir situation one relative to the other for varying the spacingbetween primary and secondary and said primary having in parallel withits terminals an ohmic resistance, which is smaller than the smallestimpedance between the primaryvterminals, the secondary coil beingaperiodically damped, and the natural wavelength of the secondary coilbeing selected to be shorter than the natural wavelength of the primarycoil, both measured in conjunction with the appertaining inherentcircuit capacities.-

5. A high frequency transformer for coupling amplifier circuits used foruniform amplifying of very wide frequency bands, more particularly fortelevision purposesfcomprising a primary and a secondary windingconnected between the circuits to be coupled and coupled so-tightly asto have a wide frequency resonance curve corresponding to the desiredwidth of frequency band produced by reason of the arising two couplingwaves, an insulated ring of conductive material, said primary andsecondary coils the resonant frequencies of which are determined by theinherent capacities being arranged in single-layer fashion co-axially onthe same axis, said primary being divided into two winding coilsarranged on either side of the secondary and wound in the samedirection, the high potential ends of one of saidprimary coils and ofthe secondary being arranged closely to one another so that theadditional capacity coupling between. said one primary coil and thesecondary is more effective between said one primary coil and saidsecondary than between the other primary coil and said secondary, saidring of conductive material being slotted in one place along a plane,passing through its' axis and being arranged movable partly over saidone primary coil and said secondary. I

KURT SCHLESINGER.

